There are many challenges for U.S. refiners to produce fuels that comply with environmental regulations and meet vehicle performance requirements. Federal and State Governments have regulated gasoline properties for many years. Generally, these regulations were developed to meet air quality goals. In 1990, the Federal Government issued the Clean Air Act Amendments, which required significant changes to gasoline used in certain areas of the United States.
Beginning Jan. 1, 1998, refiners had to certify their reformulated gasolines using the EPA Complex Model, a computer model that predicts emissions performance. The properties used in the Complex Model to predict emissions performance are: methyl tert-butyl ether (MTBE) (wt. % oxygen), ethyl tert-butyl ether (ETBE) (wt. % oxygen), Ethanol (wt. % oxygen), Methanol (wt. % oxygen), tert-amyl methyl ether (TAME) (wt. % oxygen), sulfur (ppm), Reid Vapor Pressure (psi), 50% D-86 distillation point (° F.) or E200(%), 90% D-86 distillation point (° F.) or E300(%), aromatics (vol %), olefins (vol %), and benzene (vol %).
U.S. Pat. Nos. 5,288,393, 5,593,567, 5,653,866, 5,837,126 and 6,030,521 indicate that the primary factor effecting NOx emissions is Reid Vapor Pressure (RVP), with the 10% D-86 Distillation Point and Olefins content being of secondary importance. It is reported that since reductions in 10% D-86 Distillation Point are often unacceptable for performance reasons, olefins content is generally to be used as the secondary variable in decreasing NOx emissions. These U.S. Patents report that a Reid Vapor Pressure of less than 8.0 psi and an olefins content not exceeding 15% by weight are preferred for NOx emissions reductions. These U.S. Patents also reports that 50% D-86 and distillation points not exceeding 215° F. are preferred for reducing hydrocarbon and carbon monoxide emissions.
An olefins content of less than 15% by weight is generally not difficult to achieve in high octane blends, such as 93 octane gasoline, since these fuels are generally low in olefins due to the components used to produce them. However, it is more difficult to achieve this olefins content in lower octane fuels, such as 87 octane, because of the high olefins content of the components used to produce these fuels.
An additional issue facing refiners is the pending implementation of the EPA Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur Control Requirements. Beginning in 2004, refiners must produce gasoline that averages 120 ppm sulfur with a batch limit of 300 ppm. In 2005, gasoline sulfur levels must average 90 ppm with a 300 ppm cap, and in 2006, these limits are a 30 ppm average with an 80 ppm cap.
It is desirable to produce transportation fuels that meet the emissions reductions requirements determined using EPA Complex Model and can be produced using components having a high concentration of olefins. It is further desirable to produce transportation fuels that meet the emissions reductions requirements using the EPA Complex Model and have reduced sulfur content.